Two mechanisms regulating the activity of the sodium transport system of the cell membrane are to be studied. The tissue to be used is the salt glands of the domestic duck. The glands are not normally used by the ducks but do secrete a concentrated salt solution if the ducks are maintained on saline drinking water. One mechanism to be investigated is the possible control of sodium transport by cyclic GMP. Salt secretion by the gland is stimulated by acetylcholine released from cholinergic nerves ending on the secretory cells. Our preliminary studies show that during secretion, the concentration of cyclic GMP, a known mediator for acetylcholine, is increased over 2 fold. Furthermore, we find that cyclic GMP in the presence of a soluble protein fraction from the glands will stimulate NaK-ATPase, the biochemical manifestation of the sodium transport system. Details for the examination of the mechanism and isolation of the molecular components are enclosed. The second mechanism to be examined is the control of synthesis of NaK-ATPase. The glands exhibit a large increase in Na ions transport capacity and NaK-ATPase specific activity after ducks are transferred chronically to a saline regimen. We have demonstrated that the increased enzyme activity is due to the synthesis of more enzyme protein and is not an activation effect. The synthesis and degradation of NaK-ATPase is to be examined. Attempts will be made to isolate the messenger RNA for NaK-ATPase and to study its turnover. Details are given in the proposal.